RFC 5138

A Uniform Resource Name (URN) Namespace for the Commission for the Management and Application of Geoscience Information (CGI)

Network Working Group S. Cox
Request for Comments: 5138 CSIRO
Category: Informational February 2008 A Uniform Resource Name (URN) Namespace for the Commission
for the Management and Application of Geoscience Information (CGI)
Status of This Memo
This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. Distribution of this
memo is unlimited.
Abstract
This document describes a URN (Uniform Resource Name) namespace that
is engineered by the Commission for the Management and Application of
Geoscience Information (CGI) for naming (i) persistent resources
published by the CGI and (ii) resources published by organizations
that wish them to be used in the context of services conforming to
protocols and agreements issued by CGI. The formal Namespace
Identifier (NID) is "cgi".
1. Introduction
CGI is a Commission of the International Union of Geological Sciences
(IUGS) concerned with developing best practices in the management and
application of geoscience information. The active membership is
primarily drawn from organizations with statutory responsibility for
providing geoscience information to external users (e.g., Geologic
Surveys). An important focus of activity is the development of
standards for networked data interchange to complement or supersede
the traditional map product.
A number of documents, definitions, and other artifacts, are required
to support this. CGI wishes to provide persistent,
location-independent identifiers for these resources. In addition,
organizations that subscribe to the interchange standards proposed by
CGI require external identifiers for data objects that are
transferred. CGI wishes to provide a scheme to enable data providers
to uniquely identify data, which is consistent with the requirements
of the interchange framework.
Products and services that conform to CGI endorsed interchange
specifications enable users to exchange and process geoscience
information across networks, computing platforms, and products.
Interoperability in such an environment is facilitated by the use of

a system of identifiers that is global in scope. CGI is the lead
forum for statutory organizations that act as primary providers of
technical data in this application domain.
Motivated by these concerns, CGI would like to assign formal URNs to
published resources in order to provide persistent,
location-independent identifiers for them. The process for
registering a namespace identifier is documented in [RFC3406].
The official IANA registry of URN namespaces is available online at:
<http://www.iana.org/assignments/urn-namespaces>
2. URN Specification for the "cgi" NID
Namespace ID:
cgi
Registration Information:
Registration Version Number: 1
Registration Date: 2007-10-04
Declared registrant of the namespace:
Commission for Geoscience Information (Secretariat)
c/o British Geological Survey
Kingsley Dunham Centre
Keyworth
Nottingham
Nottinghamshire
NG12 5GG
U K
Attn. Ian Jackson (ij@bgs.ac.uk)
Declaration of syntactic structure:
The Namespace Specific String (NSS) of all URNs that use the "cgi"
NID has the following structure:
urn:cgi:{CGIResource}:{ResourceSpecificString}
where the "CGIResource" is a US-ASCII string that conforms to the
URN syntax requirements [RFC2141] and defines a specific class of
resource type. Each resource type has a specific labeling scheme
that is covered by "ResourceSpecificString", which also conforms
to the naming requirements of [RFC2141].

The CGI maintains a naming authority, the CGI Naming Authority
(CGINA), that manages the assignment of CGIResource classes and
the specific registration values assigned for each resource class.
Relevant ancillary documentation:
The CGI Naming Authority (CGINA) provides information on the
registered resources and the registrations for each. More
information about CGINA and the registration activities and
procedures to be followed are available at:
<http://www.cgi-iugs.org/CGIIdentifierScheme>
A URN resolver is available at:
<http://www.cgi-iugs.org/uri>
The resolver provides a registry of CGI URNs used in CGI services.
Identifier uniqueness considerations:
The CGINA manages resources using the "cgi" NID and is the
authority for managing the resources and subsequent strings
associated. In the associated procedures, CGINA ensures the
uniqueness of the strings themselves or permits secondary
responsibility for management of well-defined sub-trees.
CGI may permit use of experimental-type values that will not be
registered. As a consequence, multiple users may end up using the
same value for separate uses. As experimental usage is only
intended for testing purposes, this should not interfere with
operational services.
Identifier persistence considerations:
CGINA provides clear documentation of the registered uses of the
"cgi" NID. This is structured such that each CGIResource has a
separate description and associated ResourceSpecificString with
separate registration tables for elements of the strings that are
separately maintained.
The registration tables and information are published and
maintained by CGINA on the CGI web site, indicated above.

Process of identifier assignment:
CGINA defines CGIResource classes used with the "cgi" NID, and
specifies the process for identifier assignment for each class.
These are described at:
<http://www.cgi-iugs.org/CGIIdentifierScheme>
and a set of registers is linked from there. Each such resource
may have three types of registration activities:
1) Registered values associated with CGI resources
2) Registration of values or sub-trees to other entities
3) Name models for use in experimental purposes
Process for Identifier Resolution:
The namespace is not listed with a Resolution Discovery System
(RDS); this is not relevant.
Rules for Lexical Equivalence:
No special considerations; the rules for lexical equivalence of
[RFC2141] apply.
Conformance with URN Syntax:
No special considerations.
Validation mechanism:
None specified. URN assignment will be handled by procedures
implemented in support of CGINA activities.
Scope:
Global
3. Examples
The following examples are representative URNs that have been
assigned by CGINA:
urn:cgi:document:CGI:CGIIdentifierScheme
- identifies the document that describes the CGI Identifier
Scheme.

urn:cgi:register:CGI:CGIResourceClasses
- identifies the register of resource classes for which
identifiers from the CGI scheme may be provided.
urn:cgi:xmlns:CGI:GeoSciML:2.0
- is the XML namespace for version 2.0 of GeoSciML, which is owned
by CGI.
urn:cgi:schema:GGIC:MineralOccurences:1.0:XMI
- identifies the XML Metadata Interchange (XMI) representation of
version 1.0 of the Mineral Occurrences information model owned
by the (Australasian) Government Geoscience Information
Committee.
urn:cgi:featureType:CGI:GeoSciML:2.0:Fault
- identifies the Fault feature-type from version 2.0 of the
GeoSciML schema that is owned by CGI.
urn:ogc:serviceType:CGI:GSML-FS:1.0
- identifies version 1.0 of the "GSML-FS" service-type owned by
CGI.
urn:cgi:classifierScheme:ICS:StratChart:2004
- identifies the 2004 edition of the Stratigraphic Chart published
by the International Commission for Stratigraphy.
urn:cgi:classifier:ICS:StratChart:2004:Silurian
- identifies the geologic period designated Silurian from the 2004
edition of the Stratigraphic Chart published by the
International Commission for Stratigraphy.
urn:cgi:classifier:GSV:Lithology:UIUYG1245NN07
- identifies the concept given the designation UIUYG1245NN07 from
the lithology scheme published by Geoscience Victoria
(Australia).

urn:cgi:feature:USGS:2feb49bc-6755-11dc-8314-0800200c9a66
- identifies a feature instance given the designation
2feb49bc-6755-11dc-8314-0800200c9a66 by the US Geological
Survey.
urn:cgi:object:SGU:552cb080-6755-11dc-8314-0800200c9a66
- identifies an object given the designation
552cb080-6755-11dc-8314-0800200c9a66 by the Geological Survey of
Sweden.
4. Namespace Considerations
There is currently no available namespace that will allow the CGI to
uniquely specify and access resources, such as schemas and
registries, that are required by organizations implementing CGI
standards. There is also a need for other standards organizations,
such as the Open Geospatial Consortium (OGC) to be able to access
CGI-specific resources.
The CGI members considered use of other existing NIDs, such as those
for OGC. However, these do not support the semantics required and in
particular do not allow for the delegation of identifier assignment
within the CGI community that is demonstrated here.
5. Community Considerations
CGI standards require access to resources, such as schemas,
registries, catalogues, documents, and services. In order for the
larger IT community to be able to implement applications that access
CGI resources effectively, a unique namespace is required. We desire
these resources to be freely and openly available as a set of
community resources.
The design of the CGI namespace builds on the experience of the Open
Geospatial Consortium (OGC) which has defined the framework of
geospatial services within which CGI standards have been developed.
The OGC membership has expertise in using the OGC URN [OGC-URN]
[OGC-DEF], gained through implementation experiments and a variety of
operational testbeds. The CGI namespace is compatible with this
experience.
6. Security Considerations
There are no additional security considerations other than those
normally associated with the use and resolution of URNs in general.

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